Pretty sure.
Manning is somewhat of an exception as he is very, very consistent. Last year he averaged 25.6 fp/g. His bad games were 11,13,14,15. Harrison averaged 17.7 fp/g (ppr) and in those 4 games he had 0,2,8,13 fpts respectively. The first 3 games would probably be losses (weeks 10, 5, 1) and the last one you would still be 14 points behind the average for your guys from those 2 players.
Brees, the number 2 last year, is probably a better example. Not counting week 17, he averaged 23 fp/g. His bad games were 7,8,9,10,11,12 fp/g. In all the rest he scored at least 22 fp/g. Hard to get a handle on his receivers as they were in and out with injuries.
Let's do 1 more. Bulger averaged 20.8 fp/g. His bad games were 15,11,10,2,1 fp/g. In those 5 games Holt scored 5,6,7,9 and 8 respectively while overall he had an average of 16 fp/g
So clearly when your QB has a bad day, his WR1 is likely to have a bad day. If you have both his WR1 and his WR2, your squad has very little chance to make up for the lost points. In the STL case, you're looking at 5 potential losses if you had QB, WR1 and WR2. In the Indy case, 3 or 4.
If you had Bulger plus Steve Smith instead of Holt, a big day by Smith could offset the bad Bulger day. Of course the risk is that both Bulger and Smith have bad days. That's a lower level risk because one performance will not influence the other.
So yes, I'm pretty sure.